Treatment of cellulosic materials such as paper and fabrics to make them resistant to water



meanest-i940 1 PATENT OFFICE F CELLULOSICQMATEBIALS SUCH AS PAPER AND FABRICS TO MAKE THEM RESISTANT TO WATER,

Thomas Lloyd, Osborne, Belvedcre,, Kent, England, asslgnor to Csllenders Cable and Construction Company Limited, London, England,

7 a British company No' Drawing.

Application May 11, 1938, Serial No. 20?,299. In Great lirltain May 24, 1937 8 Claims.

This invention is concerned with the treating oi paper, cotton fabrics and other fabrics formed from natural cellulosic materials to make them resistant to water. in accordance with the in- 9 vention the paper or fabric is dried by subjecting it to heat and o vacuum while in contact with rosin. the result of this treatment the fibres of the paper or cellulosic fabric become coated with a oi material which appears to be an ester formed by the interaction oi the cellulose and the resin, that is cellulose-rosinate. This coating reduces the water absorptive capacity of the fibrous materiel and, in the case of paper or felted fabric, gives it the power to resist the softening and disintegrating action of water.

The presence of moisture prevents the commencement or continuation of the chemical change which takes place during the treatment. Since this reaction involves the production of or fsbriclnitially to cause the reaction to start, and to continue the removal of moisture until the reaction is complete. The process of drying under vacuum is preferably continued until the absolute pressure has fallen to about 1 mm. of mercury and is carried out at a. temperature above normal atmospheric temperatures. Conveniently a temperature of about 120 C. is employed.

The resin may in general be applied in any waywhich brings it into intimate contact with the fibres of the paper or fabric. This is, of course, subject to the qualification that the method does not involve the use of any material which disadvantageously aifects the paper or fabric, either in 35 its structure or in its properties required for its subsequent use. The rosin may, for instance be applied in solution or in the form of a-suspension. Where the paper or fabric is to be' used for electrical insulating purposes it is preferable to use. a solution rather than asuspension. since the solvent can be removed whereas the dispersion agents may remain and may cause a reduction of the desired electrical properties. A solution may, for instance, be made by the aid of trichlorethyl- .ene, alcohol or other organic solvent for rosin.

Satisfactory results are obtained if the solution strength is such as to leave about 5 parts by weight of romn in 100 parts by weight of paper or fabric. when the proportion of rosin is less the waterproofing effect is correspondingly lower. However when the proportion of rosin is greater than about 5% by weight of the paper or fabric the waterproofing eflect is not correspondingly higher because the reaction is merely a surface reaction. Solutions containing from. 2 to parts water, it is therefore necessary to dry the paper by weight of rosin in 100 parts by weight oi solvent may be used. The actual strength oi solution to be employed will naturally depend upon the type of paper or fabric to be treated, the degree of waterproofing required, the time of im- 5 mersion of the material in the solution and the conditions under which the solvent is removed. It is here explained that the process by which the paper takes rosin from the solution appears to be one of adsorption. For this reason the amount adsorbed by the paper depends not only on the concentration of the rosin solution but also on the time of soaking. Thus the requisite amount of rosin can be got into the paper or fabric by soaking in 9. week solution for a. long time or by soaking it in a stronger solution for a shorter time, In general it will be satisfactory to use a solution of such a. strength that after being treated with the solution for a convenient period of time the material will contain about 5% by weight of rosin. The paper or fabric is soaked in the solution or suspension, for instance, by running it through a. bath of the solution or suspension and the solvent or suspension medium may be removed by drying in air or under a pressure less than atmospheric pressure. In the case of paper, the rosin may be incorporated in the process of manufacture of the paper, for in-- stance during the beating stage. Satisfactory results are obtained if the amount of rosin introduced into the pulp is such that the resulting paper contains about 5 parts by weight of rosin in each 100 parts by weight of paper. It may be more convenient in practice to employ a paper which has been given a. heavy rosin sizing by the paper manufacturer. Such paper, which may contain from. 5-7% of rosin is known and is to some extent already water-resistant.

The rosin-containing material thus produced or obtained is treated in accordance with the invention by heat drying it under vacuum until the reaction has been completed or substantially completed. A suitable treatment comprises drying the rosin-containing material under vacuum for a period varying from about 20 to about 50 hours-at a temperature of about 120 C., the absolute pressure at the end of the process being not greater than 1 mm. of-mercury. In general a period of about 24 hours is satisfactory but where a higher degree of waterproofing is required the drying may be continued for a longer period say for about 50 hours. Further drying beyond a period of about 50 hours produces little increase in the waterproofing eflect. The treatment may be applied to the paper or fabric while it is in roll form. This will generally be more convenient in view of the prolonged time of treatment than a treatment in which the material is fed continuously through a drying oven.

To provide an indication of the water-resistant property imparted to paper by the process in accordance with the invention, the following test procedure has been adopted. A test specimen of paper is soaked in distilled water at 20 C.; at the end of this period the specimen is quickly transferred to a tensile testing machine and the breaking load determined. The degree of waterproofing is taken to be the breaking load when wet as a percentage of the breaking load when dry. By this method the following figures are obtained:

1 Per cent Paper as received from manufacture 9 Paper soaked in 5% rosin solution in trichlorethylene and dried in air 19 The above rosin-treated paper after treatment in accordance with the invention What I claim as my invention is:

1. A process for rendering resistant to water a material consisting of paper or cotton or other fabric formed from natural cellulosic material, which process comprises drying the material and forming on the fibres thereof a film of cellulose rosinate by subjecting it to heat and a vacuum whilst the fibres are in intimate contact with rosin.

2. A process for rendering resistant to water a material consisting of paper or cotton or other fabric formed from natural cellulosic material, which process comprises soaking the material in a solution of rosin, drying the material to remove the solvent therefrom, and then drying the material and forming on the fibres thereof a film of cellulose rosinate by subjecting it to heat and a vacuum.

3. A process for rendering resistant to water a. material consisting of paper or cotton or other fabric formed from natural cellulosic material, which process comprises soaking the material in a suspension of rosin, drying the material to remove the suspension medium, and then forming on the fibres thereof a film of cellulose rosinate by subjecting it to heat and a vacuum.

4. A process for rendering resistant to water a material consisting of paper or cotton or other fabric formed from natural cellulosic material, which process comprises adding a suspension of rosin -to the material at the beating stage of its manufacture and drying the resulting rosincontaining material and converting the surfaces of the fibres thereof into cellulose rosinate by subjecting it to heat and a vacuum.

5. A process for rendering more resistant to water a material, which consists of paper or cotton or other fabric formed from natural cellulosic material and contains about 5 parts by weight of rosin in each parts by weight of the material, which process comprises drying the rosin-containing material and converting the rosin-coated surfaces of the fibres thereof into cellulose rosinate by subjecting it to heat and a vacuum.

6. A process for rendering more resistant to water, a material which consists of paper or cotton or other fabric formed from natural cellulosic material and contains up to about 5 parts by weight of rosin in each 100 parts by weight of material, which process comprises drying the rosin-containing material for from 20 to 50 hours at a temperature of about C. at an absolute pressure'which' at the end of the process is not greater than 1' mm. of mercury.

'7. As a new article of manufacture, a liquid pervious material which consists of paper or cotton or other fabric formed from natural cellulosic material and of which the fibres individually consist of a core of natural cellulosic material and an enveloping skin consisting of the reaction product of the surface cellulose of the fibre and rosin.

8. As a new article of manufacture, a liquidpervious; water-resistant material in sheet form, which consists of superficially rosin esterified cellulose fibres.

THOMAS OSBORNE. 

